It depends on what I want to read. For newer titles, I rent maybe 95% of the time. Just a couple of weeks ago I went to my library and rented an entire series that just came out last year. Thankfully I have multiple well-stocked libraries in my county to make this possible, since I prefer holding physical books.

If I want to read a book that's been out for a while, I buy maybe 50% of the time. If I know there's a high chance that I'll like it and I can find it for a low price secondhand, I'll add it to my home library. Ebay and thriftbooks are great for getting super cheap books. I also tend to pick up random books for a buck on clearance at half price books or at a library donation bookstore.